Effector memory T cells, early metastasis, and survival in colorectal cancer.

BACKGROUND: The role of tumor-infiltrating immune cells in the early metastatic invasion of colorectal cancer is unknown. METHODS: We studied pathological signs of early metastatic invasion (venous emboli and lymphatic and perineural invasion) in 959 specimens of resected colorectal cancer. The local immune response within the tumor was studied by flow cytometry (39 tumors), low-density-array real-time polymerase-chain-reaction assay (75 tumors), and tissue microarrays (415 tumors). RESULTS: Univariate analysis showed significant differences in disease-free and overall survival according to the presence or absence of histologic signs of early metastatic invasion (P<0.001). Multivariate Cox analysis showed that an early conventional pathological tumor-node-metastasis stage (P<0.001) and the absence of early metastatic invasion (P=0.04) were independently associated with increased survival. As compared with tumors with signs of early metastatic invasion, tumors without such signs had increased infiltrates of immune cells and increased levels of messenger RNA (mRNA) for products of type 1 helper effector T cells (CD8, T-BET [T-box transcription factor 21], interferon regulatory factor 1, interferon-gamma, granulysin, and granzyme B) but not increased levels of inflammatory mediators or immunosuppressive molecules. The two types of tumors had significant differences in the levels of expression of 65 combinations of T-cell markers, and hierarchical clustering showed that markers of T-cell migration, activation, and differentiation were increased in tumors without signs of early metastatic invasion. The latter type of tumors also had increased numbers of CD8+ T cells, ranging from early memory (CD45RO+CCR7-CD28+CD27+) to effector memory (CD45RO+CCR7-CD28-CD27-) T cells. The presence of high levels of infiltrating memory CD45RO+ cells, evaluated immunohistochemically, correlated with the absence of signs of early metastatic invasion, a less advanced pathological stage, and increased survival. CONCLUSIONS: Signs of an immune response within colorectal cancers are associated with the absence of pathological evidence of early metastatic invasion and with prolonged survival.

Small bowel diverticulosis complicated by perforated jejunal diverticula: conservative and/or surgical management?

Small Bowel Diverticulosis (SBD) is rare and defined by the presence of multiple acquired mucosal herniations on the layer of the duodenal or jejunoileal loop. Usually asymptomatic, SBD is revealed by complications in 5 to 10% of cases. We report two cases of SBD complicated by perforated diverticula. The first case of perforation, revealed by an inflammatory anemia, required a surgical resection after failure of the first-intent medical treatment. The second case, revealed by fever and abdominal pain, was successfully managed by medical treatment. In case of SBD perforation, surgical management should be proposed as first-intent treatment in case of generalized peritonitis or after failure of first-intent medical treatment applied to localized peritonitis.

Endoscopic management of a large choledochocele associated with choledocholithiasis.

Choledochocele or type III choledochal cyst is a very rare lesion, defined as a cystic dilatation of the distal common bile duct protruding into the duodenal lumen. Abdominal pain, biliary disorders, and acute pancreatitis are frequently observed but malignant degeneration is rare. A 70-year-old man had a history of epigastralgia associated with abnormal liver function tests suggesting gallstones. During laparoscopic cholecystectomy, intraoperative cholangiography showed a 40-mm-diameter choledochocele associated with choledocholithiasis. A transcystic drain was placed after cholecystectomy had been completed. Endoscopic retrograde cholangiopancreatography confirmed the diagnosis and a 45-mm-long endoscopic sphincterotomy successfully treated both lesions as confirmed by a transcystic cholangiogram showing a thin-walled common bile duct with no residual stones. This case illustrates that the diagnosis of choledochocele remains difficult in clinical practice and confirms that endoscopic retrograde cholangiopancreatography is the best available diagnostic tool. Coexistent choledocholithiasis is observed in about 20% of choledochocele. Endoscopic sphincterotomy is feasible and effectively treats both lesions even in larger choledochoceles.

Long-term prognostic value of detection of circulating colorectal cancer cells using CGM2 reverse transcriptase-polymerase chain reaction assay.

BACKGROUND: The criteria commonly used for prognosis of colorectal cancer remain histoprognostic and are based on primarily TNM classification. The lack of discrimination of purely histoprognostic criteria is evidenced by the development of different outcomes in similarly staged patients. The aim of this work was to study the long-term prognostic value of preoperative detection of circulating enterocytes in the blood of colorectal cancer patients using the CGM2 reverse transcriptase-polymerase chain reaction (RT-PCR) assay. METHODS: A nested RT-PCR with specific primers for CGM2 was used preoperatively to detect circulating enterocytes in 121 patients (64 men, 57 women; mean age, 70 years) with colorectal neoplasms. RESULTS: Circulating enterocytes were detected in 58/121 (48%) patients. The positivity rate was not correlated with American Joint Committee on Cancer (AJCC) staging (stage I, 11/28 (39%); stage II, 13/34 (38%); stage III, 15/23 (65%); stage IV, 17/32 (53%); sterilized (after radiotherapy, no residual neoplasm) 2/4 (50%); not significant [NS]), but circulating enterocytes were detected more frequently in patients with metastatic lymph nodes (60% vs 41%, P = .06). Overall 5-year survival rates (mean +/- SD) were 40 +/- 13% and 45 +/- 13% for patients without and with circulating enterocytes, respectively (P = NS). Similarly, recurrence-free survival rates were 71 +/- 4% versus 72 +/- 14% (P = NS). Using univariate analysis, AJCC stage (P < .0001) was correlated with survival. AJCC stage (P = .007) and obstructive neoplasms (P = .043) were correlated with recurrence-free survival. Using multivariate analysis, AJCC stage was correlated with survival and recurrence-free survival. CONCLUSIONS: Preoperative detection of circulating enterocytes using CGM2 RT-PCR assay provides no specific prognostic information and cannot be used as a decision criterion for adjuvant therapy.

Sonic Hedgehog-dependent proliferation in a series of patients with colorectal cancer.

BACKGROUND: The Hedgehog (Hh) gene family is known to regulate development of stem cells. In addition, activation is responsible for the induction of GLI1 proto-oncogene and subsequent cellular proliferation. Sonic Hedgehog (SHh), one of the Hh family members promotes carcinogenesis in airway and pancreatic epithelia, is expressed in colonic stem cells. As differentiated colonic cells arise from constant renewal of Hedgehog-expressing colonic stem cells, SHh could be involved in human colonic carcinogenesis. METHODS: Tissue samples of colorectal adenocarcinoma (T) and adjacent normal colon tissue (NT) were sampled from each of 44 consecutive patients with colorectal cancer. Specific transcription of SHh, GLI1, and the GLI1 downstream target FOXM1 were evaluated using semiquantitative reverse transcriptase polymerase chain reaction. Similar in vitro measurements of mRNA of GLI1 and FOXM1 transcription levels after specific induction by SHh-Np were performed in the HT-29 colorectal tumor cell line to confirm the in vivo results. RESULTS: SHh mRNA was overexpressed in colorectal adenocarcinomas in 38 of 44 (86%) patients. Expression of transcription levels of GLI1 and FOXM1 correlated with SHh expression (SHh vs GLI1, r = 0.77, P < .0001; GLI1 vs FOXM1, r = 0.68, P < .0001; SHh vs FOXM1, r = 0.79, P < .0001). SHh overexpression did not appear to correlate with the patient characteristics evaluated. Similarly, when studied in the HT-29 colorectal cell line, exogenous SHh promoted cell proliferation, while inhibition of SHh expression decreased proliferation. Expression of GLI1 and FOXM1 mRNA increased with exogenous exposure to SHh. CONCLUSIONS: We demonstrated increased expression of SHh mRNA in human colonic adenocarcinomas and in a colorectal cell line with downstream increased expression of GLI1 and FOXM1 mRNA known to promote cell proliferation. This upregulation within human colorectal adenocarcinoma tissue confirms the potential role of the Hh pathway in colorectal carcinogenesis and suggests a potential therapeutic target of Hh blockade in colorectal cancer.

Prognostic significance of MMP-1 and MMP-3 functional promoter polymorphisms in colorectal cancer.

PURPOSE: Matrix metalloproteinase (MMP) belongs to a large group of proteases capable of breaking essentially all components of the extracellular matrix. They are implicated in all steps of tumorogenesis, cancer invasion, and metastasis. Among them, metalloproteinase type 1 (MMP-1) is implicated in tumor invasion and metastasis in different types of cancers including colorectal cancer in which its expression was correlated with poor prognosis. A polymorphism in the promoter region of the MMP-1 gene leads to a variation of its level of transcription. STUDY DESIGN: MMP-1 -1607ins/delG and MMP-3 - 1612 ins/delA promoter polymorphisms were genotyped by multiplex PCR from 201 colorectal cancer patients. The median follow-up of patients was 30 months. The MMP genotypes were correlated to clinical outcome. RESULTS: Patients with the -1607insG/-1607insG MMP-1 genotype had significantly worse specific survival than the others in the whole series (P < 0.04), in stage I to III patients (P < 0.001), and in patients stage I and II (P < 0.01). In multivariate analysis, MMP-1-1607insG allele showed to be an independent poor prognostic factor after adjustment on stage, age, and the use of adjuvant chemotherapy. MMP-3 polymorphism was not associated with survival. CONCLUSIONS: In the subgroups of nondistant metatastic patients (stages I and II, and stages I-III), an inverse relation between the number of MMP-1-1607insG allele and survival was observed suggesting a gene dosage effect. Our results are consistent with the importance of MMP-1-1607ins/delG functional polymorphism in regulating transcription level and with the relationship between MMP-1 expression and cancer invasion, metastasis, and prognosis.

Thymidylate synthase gene polymorphism predicts toxicity in colorectal cancer patients receiving 5-fluorouracil-based chemotherapy.

PURPOSE: The target enzyme for 5-fluorouracil (5-FU) is thymidylate synthase (TS). The TYMS gene encoding this enzyme is polymorphic, having either double (2R) or tri-tandem (3R) repeats of a 28-bp sequence in the promoter region and a 6-bp variation in the 3'-untranslated region (3'-UTR). TS expression predicts response to 5-FU-based chemotherapy, and the expression seems to be determined by the TYMS gene promoter. The aim of this study was to investigate the utility of determining these two TYMS gene polymorphisms to predict the toxicity and efficacy of 5-FU treatment in patients with colorectal cancer. EXPERIMENTAL DESIGN: The determination of TYMS genotypes was performed in tumor and normal tissues by PCR amplification from 90 patients with colorectal cancer who were treated with adjuvant or palliative 5-FU-based chemotherapy. Associations between polymorphisms in the TYMS promoter and in the 3'-UTR gene and clinical outcome of these 90 patients treated with 5-FU based chemotherapy were evaluated individually. The linkage between TYMS promoter and TYMS 3'-UTR region polymorphisms was evaluated and a haplotype analysis was performed. RESULTS: Individuals who were homozygous for the double repeat in the TYMS promoter region had more severe side effects to 5-FU. Patients with a 2R/2R, a 2R/3R, or a 3R/3R genotype had a grade 3 or 4 toxicity rate of 43, 18, and 3% respectively (P < 0.01). The TYMS promoter and TYMS 3'-UTR polymorphisms were in linkage disequilibrium, and the haplotype 2R/ins 6-bp was significantly associated with a high risk of severe side effects to 5-FU. The TYMS promoter and TYMS 3'-UTR polymorphisms were not associated with a response to 5-FU and survival of patients who received palliative 5-FU-based chemotherapy. CONCLUSIONS: This study demonstrated that TYMS genotyping could be of help in predicting toxicity to 5-FU-based chemotherapy. TYMS genotyping might make it possible to individualize treatment for patients with colorectal cancer.

Complications after laparoscopic adjustable gastric banding for morbid obesity: experience with 1,000 patients over 7 years.

BACKGROUND: Laparoscopic adjustable gastric banding (LAGB) is considered the least invasive surgical option for morbid obesity. It is less efficient than gastric bypass in weight loss, but has the advantage of being potentially reversible and can improve the quality of life if mortality and morbidity are low. METHODS: Between 1996 and 2003, 1,000 patients underwent LAGB. There were 896 women and 104 men with mean age 40.4 years (16.3-66.3). Preoperative mean BMI was 44.3 kg/m(2). RESULTS: There were no deaths. Cumulative rate of complications was 192 (19.2%). 12 were life-threatening (1.2%): gastric perforation (n=4), acute respiratory distress (n=2), pulmonary embolism (n=2), migration (n=3), and gastric necrosis (n=1). 111 patients required an abdominal reoperation (11.1%) for perforation (n=2), slippage (n=78), migration (n=3), necrosis (n=1), esophageal dilatation (n=2), incisional hernias (n=4) and port problems (n=21). Before October 2000, we used the perigastric technique, and the slippage rate was 24% (91 / 378 ).Then, we changed to the pars flaccida approach and the slippage rate fell to 2% (13 / 622). The pars flaccida approach demonstrated safety in relation to both risks of perforation and slippage. CONCLUSION: The cumulative complication rate increased to 3-4 years, and then decreased with experience and technical improvement. Concerns of long-term follow-up should be migration and esophageal dilatation, which seem to be rare at 3 years.

Role of intraoperative enteroscopy in the management of obscure gastointestinal bleeding at the time of video-capsule endoscopy.

BACKGROUND: This study aimed at evaluating the role of intraoperative enteroscopy (IOE) for the management of obscure gastrointestinal (GI) bleeding in patients who had been preoperatively explored by video-capsule endoscopy (VCE). METHODS: Eighteen patients who underwent IOE for obscure GI bleeding were prospectively recorded between November 2000 and January 2007. The bleeding site was preoperatively localized by VCE in the small bowel in 15 patients, but the origin of bleeding remained unknown in 3 patients. RESULTS: In the 3 patients with negative VCE, IOE was normal, but intraoperative conventional endoscopy identified gastric (n = 1) and colonic (n = 2) lesions. Among the 15 patients with VCE positive for small-bowel lesions, laparotomy and IOE yielded localization and treatment (surgical n = 11 and endoscopic n = 2) guidance for 13 of 15 (87%) lesions. At median 19-month follow-up, 3 bleeding recurrences (3 of 15 [20%]) were recorded, resulting in a 73% therapeutic efficacy of IOE. CONCLUSIONS: IOE remains useful for the management of obscure GI bleeding when preoperative VCE is positive for small-bowel lesions that are not reachable by nonoperative enteroscopy. When VCE is negative, new conventional endoscopy should be proposed instead of IOE.

Liver hanging maneuver: an anatomic and clinical review.

BACKGROUND: Liver hanging maneuver (LHM) allows to hang the liver during right hepatectomies without primary liver mobilization. The avascular plane used in this technique has been poorly described in the anatomical literature, and intraoperative bleeding because of hepatic vein injuries has been reported. DATA SOURCES: Major clinical and anatomic articles focusing on the retrohepatic portion of the inferior vena cava (IVC) and the LHM were reviewed. CONCLUSIONS: LHM is as an effective and safe method of guiding hepatic transection to the IVC during right hepatectomies with a feasibility rate up to 95% and minor bleeding in 0% to 6% of cases. According to small series and experts' opinions, LHM would improve parenchymal transection by reducing operative time and blood loss. The tape would ensure a linearly cut surface with IVC safer protection, better exposure, and hemostasis of the deeper plane. Limited remnant liver mobilization could reduce the risk for malignant dissemination and improve liver function. Hepatectomies for huge tumor with diaphragm adhesions could be facilitated.

Clinical interest of digestive arterial trunk anastomoses.

Arterial vascularization of the gastrointestinal tract is a three-level system composed of the coeliac trunk, and both superior and inferior mesenteric arteries. The three levels are joined together via arterial trunk anastomoses such as the so-called and well-known Riolan arcade or supramarginal arcade. The aim of this study was to review the embryology of the digestive arteries in order to understand the anatomic variations, the development of the arterial trunk anastomoses and the potential collateral circulation in the case of obstruction of one or several arterial trunks. The arch theory by Mac Kay and Tandler longitudinal arterial anastomosis account for the genesis of the arterial trunk anastomoses and the main anatomic variations. The coeliac trunk and the superior mesenteric artery are joined together via the pancreaticoduodenal arcades and the Bühler arcade. These anastomoses are divided during pancreatic resections but developed in the case of coeliac trunk stenosis. The mesenteric arteries are joined together by the Riolan, Villemin arcades and by the marginal artery of Drummond. This collateral circulation and the Riolan arcade in particular, is utilized during left colonic resection. In the case of this collateral circulation insufficiency, inferior mesenteric artery reimplantation is necessary during abdominal aortic aneurysmectomy. Arteriopathy, more and more frequent due to population ageing is responsible for frequent obliteration of one or several digestive arterial trunks with subsequent development of collateral circulation. For such reasons, a sound knowledge of digestive arterial anatomy is an absolute prerequisite for surgical practice.

Laparoscopic detection of aberrant left hepatic artery: a prospective study in 300 consecutive patients.

Laparoscopic gastric banding comprises the systematic section of the pars flaccida and condensa of the lesser omentum. Aberrant left hepatic arteries (ALHA) originating from the left gastric artery are located in the pars condensa of the lesser omentum. The aim of the present work was to study aberrant left hepatic artery rate in a prospective series of patients operated on for morbid obesity using laparoscopic gastric banding. Between October 2001 and December 2003, a monocentric prospective study of 300 consecutive patients operated on for morbid obesity was carried out. There were 245 women and 55 men with a mean age of 39+/-11 years. Preoperative weight was 123+/-18 kg, mean size was 166+/-9 cm and preoperative mean BMI was 44.5+/-5.6 kg m(-2) . Data were collected intraoperatively using a questionnaire submitted to the surgeon with patient and ALHA characteristics. The ALHA were detected in 102 patients (34%): one ALHA in 100 cases (98%) and two ALHA in two cases (2%). The ALHA diameter was estimated by comparison using laparoscopic instruments. The median ALHA diameter was 2 mm (0.5-13). A diameter >or=3 mm was observed in 47 patients (16%) and

Type, density, and location of immune cells within human colorectal tumors predict clinical outcome.

The role of the adaptive immune response in controlling the growth and recurrence of human tumors has been controversial. We characterized the tumor-infiltrating immune cells in large cohorts of human colorectal cancers by gene expression profiling and in situ immunohistochemical staining. Collectively, the immunological data (the type, density, and location of immune cells within the tumor samples) were found to be a better predictor of patient survival than the histopathological methods currently used to stage colorectal cancer. The results were validated in two additional patient populations. These data support the hypothesis that the adaptive immune response influences the behavior of human tumors. In situ analysis of tumor-infiltrating immune cells may therefore be a valuable prognostic tool in the treatment of colorectal cancer and possibly other malignancies.

Chromoendoscopic colonoscopy for detecting preneoplastic lesions in hereditary nonpolyposis colorectal cancer syndrome.

BACKGROUND & AIMS: In hereditary nonpolyposis colorectal cancer (HNPCC) syndrome, flat and small adenomas are particularly prone to malignant transformation but might be missed by standard colonoscopy. We prospectively studied the diagnostic yield of high-resolution colonoscopy coupled with chromoendoscopy for preneoplastic and neoplastic colorectal lesions in patients with HNPCC syndrome. METHODS: Thirty-six consecutive asymptomatic patients (mean age, 42 years) belonging to HNPCC families and receiving genetic counseling were enrolled in this prospective study. Colonoscopy was performed in 2 steps. Conventional colonoscopy was performed first, followed by a second colonoscopy with chromoendoscopy with indigo carmine (.4%) dye sprayed onto the entire proximal colon. RESULTS: Conventional colonoscopy identified 25 lesions (mean size, 4 +/- 3 mm) in 13 patients. Seven lesions, detected in 5 patients, were adenomas, 3 of which were located in the proximal colon. Chromoendoscopy identified additional 45 lesions (mean size, 3 +/- 1 mm) in 20 patients; most of these lesions were flat and hyperplastic. Eleven additional adenomas were detected in the proximal colon of 8 patients, and 8 of these 11 lesions were flat. The use of chromoendoscopy significantly increased the detection rate of adenomas in the proximal colon, from 3 of 33 patients to 10 of 33 patients (P = .045). CONCLUSION: Relative to conventional colonoscopy, high-resolution colonoscopy with chromoendoscopy markedly improves the detection of adenomas in patients with HNPCC syndrome and might help to prevent colorectal carcinoma in these patients with a very high risk of colorectal cancer.

Immunobead multiplex RT-PCR detection of carcinoembryonic genes expressing cells in the blood of colorectal cancer patients.

Circulating cell detection using reverse transcriptase-polymerase chain reaction (RT-PCR) techniques has been studied as a new prognostic factor in colorectal cancer patients. With the view of enhancing detection sensitivity, we developed a new multiplex RT-PCR assay for circulating cell detection based on the expression of carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5; formerly CEA) and CEACAM7 (formerly CGM2). Between November 2002 and December 2003, 45 stage III-IV, 39 stage I-II colorectal cancer patients, 32 non-colorectal cancer patients and 41 healthy individuals were included. Positive selection using HEA-125 immunobeads was applied to blood samples before mRNA extraction, cDNA synthesis and a multiplex CEACAM5/CEACAM7 RT-PCR assay. For both CEACAM5 and CEACAM7, the limit of detection was found to be as low as 1 expressing cell in 10(6) nucleated blood cells. The multiplex RT-PCR assay was negative for the 41 healthy individuals and the 32 non-colorectal cancer patients. The test was positive in 53/84 (63%) of the colorectal cancer patients for CEACAM5 and/or CEACAM7, whereas 32/84 (38%) were positive for both markers. Colorectal cancer patients were positive for one of the two markers in 80% of cases (36/45) for stage III-IV patients (CEACAM5 73%, CEACAM7 51%) and in 44% of cases (17/39) for stage I-II patients. This multiplex RT-PCR assay with two markers proved to be more sensitive than use of a single marker in detecting circulating tumour cells. The discrepant expression of CEACAM5 and CEACAM7 may label circulating tumour cells that have different levels of differentiation and subsequent aggressive behaviour.

Detection of free-circulating tumor-associated DNA in plasma of colorectal cancer patients and its association with prognosis.

Tumor cells are characterized by specific genetic alterations. When such genetic alterations are identified in body fluid including plasma, regardless of the presence of detectable tumor cells, it shows the existence of free-circulating tumor-associated DNA. The objective of our study was to assess the prognostic value of free-circulating tumor-associated DNA in colorectal cancer patients' plasma. The first step of our work was to find common genetic alterations in tumors that would subsequently be used for plasma DNA screening. We focused on KRAS2 mutations in codons 12 and 13 by the mutant allele-specific amplification (MASA) method and p16 hypermethylation by the methylation-specific polymerase chain reaction (MSP) method. Patients with a tumor presenting either alteration were selected for plasma screening; 58 tumors were analyzed for KRAS2 mutations and tested for p16 gene promoter methylation. Survival and recurrence rates were assessed in patients with and without free-circulating tumor-associated DNA alterations in plasma. Of the 58 tumors analyzed, 39 (67%) demonstrated either one or both of the studied genetic alterations. Twenty-two (38%) were mutated at KRAS2, and an identical alteration was detected in 10 (45%) of the 22 corresponding plasma samples. Thirty-one (53%) had p16 gene promoter hypermethylation that could also be detected in the plasma in 21 cases (68%). Among the 39 patients who had one or the other alteration in tumor DNA, 37 had at least one reliable plasma test. In 26 (70%) of the 37 patients, free-circulating tumor-associated DNA was detected in plasma. The 2-year overall survival rate was 48% in the group where free-circulating tumor-associated DNA was detected in plasma and 100% in the one where free-circulating tumor-associated DNA was not detected in plasma (p < 0.03). Among these 37 patients, 25 patients had a stage I, II or III disease. In this subgroup of patients, the 2-year recurrence-free survival rate for the 17 patients with free-circulating tumor-associated DNA detected in plasma was 66%, compared to 100% for the 8 patients without free-circulating tumor-associated DNA detected in plasma (p = 0.044). The presence of free-circulating tumor-associated DNA in plasma seems to be a relevant prognostic marker for patients with colorectal cancer and may be used to identify patients with a high risk of recurrence.

Frequent mutations of hepatocyte nuclear factor 1 in colorectal cancer with microsatellite instability.

BACKGROUND & AIMS: The TCF1 gene encoding hepatocyte nuclear factor 1 alpha (HNF1), a transcription factor germline mutated in patients with maturity-onset diabetes of the young type 3, was recently found to be frequently inactivated by biallelic alterations in liver adenoma and in rare hepatocellular carcinomas. The impact of HNF1 in colorectal carcinogenesis has not been studied until now. Colorectal cancer is characterized by the existence of different molecular mechanisms known as microsatellite stable or unstable tumors. METHODS: At first, a series of 10 adenomas and 29 colon cancers regardless of microsatellite instability status were screened for TCF1 mutations on the entire coding sequence. RESULTS: Three mutations in microsatellite instability high (MSI-H) tumors were found in the exon 4 polymorphic poly-cytosin (C)(8) or (C)(9) tract and consisted of a cytosin deletion at position 291. To further characterize the prevalence of TCF1 mutations in the subgroup of MSI-H tumors, 52 additional MSI-H samples were screened for exon 4 alterations; 23% of MSI-H tumors (95% confidence interval, 14%-36%) were found to harbor frameshift at the poly-cytosin tract. The (C)(9) allele was significantly more frequently mutated than the (C)(8) allele (22% vs. 8%; P = 0.03), showing a higher instability of the longer repetition. CONCLUSIONS: These results show a role for HNF1 in MSI-H colorectal carcinogenesis.